Reference is made to U.S. Pat. No. 3,619,254 (Davis), which is directed to thermometric articles and methods for preparing same. Such patent describes an article in which a cholesteric liquid crystal material is supported on a substrate; the cholesteric liquid crystal material provides a color response as a function of temperature thereof. The cholesteric liquid crystal material scatters white light to give respective colors as a function of the temperature of the liquid crystal material. U.S. Pat. No. 4,022,706 (Davis) is another example of a disclosure of use of cholesteric liquid crystal material that provides a color response as a function of temperature. Specific formulations are described therein. The disclosures of such patents hereby are incorporated by reference.
In the past liquid crystal devices have been used for identifying the temperature of a device, a part, an environment, and even the human body, the latter sometimes referred to as thermal mapping of the body. Such identification has been accomplished using liquid crystal material that provides a color response such that different colors represent different respective temperatures. For example, a device containing the liquid crystal material would be held in intimate engagement with a part being examined. After temperature stabilization such that the temperatures of various areas of the device would be representative of the temperatures of the immediately underlying surface of such part, the color(s) presented by the respective areas of the device would indicate the relative temperature(s) of the part.
Importantly, the ability to detect relative temperature of the body may be used as a tool to detect possible medical problems. For example, liquid crystal devices to which the present invention relates have been used in the past as a tool to detect possible cancer, for the temperature of unhealthy tissue frequently is different from the temperature of healthy tissue. The present invention may be used for breast thermography, for example, to detect breast cancer or other possible problems regarding the breast(s) by providing an optical means, preferably by color, to make a comparison of the temperatures associated with the tissue of both breasts simultaneously. Ordinarily the temperature patterns of both breasts should be approximately symmetrical. A noticeable difference between the temperature patterns of both breasts may indicate the possibility of a problem. As will be apparent from the description herein, the present invention may be used for such medical and for other medical purposes when temperature information is desired.
The ability to detect the temperature of various devices, parts, etc. also is particularly useful to indicate overheat, near overheat, too cold, correct, etc. conditions. For example, if a motor were too hot, burn out is possible; and it would be desirable to indicate the hot condition so the motor could be shut down before damage occurs.
Liquid crystal thermometers are known. In one such thermometer device a particular number becomes visible to indicate that the thermometer is at such temperature. Reference is made, for example, to Seto et al. U.S. Pat. No. 3,704,625 and to Parker U.S. Pat. No. 3,861,213.
A difficulty encountered in the above-mentioned and in various liquid crystal temperature indicating devices, has been the limited number of colors in which the liquid crystal material can respond and/or the particular temperature range within which such colors must respond to indicate respective temperature. A corollary difficulty relates to the trade-off needed between accuracy of temperature indication and operational range. Increasing accuracy reduces range because the several colors are needed precisely to indicate relatively close temperatures. Increasing range, then, would reduce accuracy. To accomodate such difficulty, in the past several liquid crystal devices, each having a different temperature range had to be used sequentially until an accurate indication of temperature is achieved. Alternatively, a multiple event device, say two events, having two superimposed layers of temperature responsive color producing liquid crystal material has been used. Each liquid crystal material would have a color response in a different respective temperature range. The liquid crystal material may be transparent and uncolored when the temperature thereof is outside the respective temperature range at which color response is provided. The problem encountered using such multiple event detection device has been the difficulty in determining which of the liquid crystal materials is in its color response operational temperature range.